1. Field of the Invention
The present invention relates to a method of cleaning a film-forming apparatus and a film-forming apparatus equipped with a cleaning system, and more particularly, a method and a film-forming apparatus for cleaning off a silicon-based deposits including silicon oxide or silicon nitride deposited in the film-forming apparatus.
2. Description of the Related Art
In manufacturing a semiconductor device, various (insulating) thin films such as a silicon dioxide film or a silicon nitride film are formed by using a film-forming apparatus comprising a chemical vapor deposition reaction chamber (CVD reaction chamber). In forming the thin film, the CVD reaction product is deposited not only on the surface of a target semiconductor wafer but also on the constituent member of the film-forming apparatus such as the wall of the CVD reaction chamber, the boat or susceptor for supporting the semiconductor wafer, or piping. The CVD reaction product deposited on the constituent members, if left unremoved, peels off from, for example, the inner wall of the CVD reaction chamber. This generates particles and results in degrading the semiconductor thin film formed on the wafer by the CVD reaction in the subsequent step. Thus, it is necessary to clean the film-forming apparatus.
For example, Japanese Patent No. 3014368 discloses the use of a cleaning gas consisting of hypofluoride gas such as CF3OF, optionally added with an oxygen-containing gas, to clean off silicon oxide or silicon nitride. Jpn. Pat. Appln. KOKAI Publication 2002-158181 disclose the use of a cleaning gas consisting of COF2 gas added with oxygen gas. Further, Jpn. Pat. Appln. KOKAI Publication 2002-18476 discloses the use of a cleaning gas consisting of COF2 added with an additive gas such as fluorine gas.
More specifically, in the prior art techniques mentioned above, the cleaning gas is excited by means of a plasma, which is then subjected to the cleaning of the silicon-based deposits such as silicon oxide. However, as the plasma damages the constituent members of the film-forming apparatus, it is necessary to take measures to protect the constituent members. Further, plasma is unstable by itself and high in reactivity, and thus is difficult to control.
By contrast, in a thermal cleaning in which silicon-based deposits are cleaned off by the reaction of the silicon-based deposits with a cleaning gas under heat (thermal reaction), the cleaning can be controlled by the temperature in the cleaning, and the reactivity is not so high as to damage the constituent members of the film-forming apparatus.
However, the present inventors have found that the prior art cleaning gases described above can not perform a cleaning of silicon-based deposits sufficiently by heating alone, without using a plasma.